1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to a heat exchange arrangement in a fan duct of a gas turbine engine for cooling high pressure hot bleed air.
2. Description of the Prior Art
Many commercial aircraft gas turbine engines employ high pressure hot air bled from the core engine compressor for use by different systems on the aircraft. In particular, the high pressure air is required by a variety of tasks on the aircraft, such as anti-icing and passenger cabin cooling. However, prior to use of the air, the temperature of the air must be lowered to reasonable levels in accordance with the requirements of each specific task.
One current method of cooling the high pressure compressor bleed air is to extract or bleed air from the engine fan duct aft of the outlet guide vanes of the engine nacelle. The cooler bleed air from the fan duct and the high pressure hotter bleed air from the core engine compressor are then passed through a heat exchanger where the hotter high pressure air gives up some of its thermal energy to the cooler fan duct bleed air.
Use of the heat exchange process is necessary, although, current systems for attaining heat transfers are unduly complex. In one system, an elaborate layout of piping is employed to pass the high pressure bleed air to the aircraft and to route the cooler fan duct bleed air to the location of the heat exchanger. By the time the cooler fan duct bleed air reaches the heat exchanger and performs its cooling task, it has lost most of its pressure (thrust potential) due to frictional losses because of various bends and turns of the piping. After exiting from the heat exchanger, the fan duct bleed air is discharged overboard from the aircraft structure with a negligible thrust benefit. The impact of the fan duct bleed air thrust loss on engine specific fuel consumption is significant. Furthermore, the excessively complex bleed air piping adds significantly to the aircraft weight.
Consequently, a need still remains for improvements in the arrangement for performing heat transfer operations which will avoid the fan duct bleed air loss experienced by the prior art.